Flow regulating valves are devices that can be adjusted to restrict or increase the flow of a fluid through a conduit. Such valves are generally well known in the art and have many practical applications. For example, in the commercial natural gas production industry, flow-regulating valves are commonly used to vary the flow of natural gas through a network of gas collection pipes. The network of collection pipes will often connect and branch together tens to hundreds of natural gas ground wells in a localized geographic region. The individual wells will feed natural gas through the network of gas collection pipes to a common output location. Often, the desired natural gas output is less than the maximum production capacity of the several wells combined. Such demands can change due to cyclical seasonal trends and for other economic reasons. This creates a need for regulating and monitoring natural gas production from each well to control the supply.
A branch collection pipe for each individual well typically includes a flow-regulating valve and a gas flow sensor arranged in fluid series to regulate the production output of each individual well. The gas flow sensor indicates the amount of natural gas that flows through the collection pipe. The regulating control valve provides a variable degree of opening that forms a restriction orifice in the collection pipe and thereby sets the natural gas flow rate in the collection pipe.
The flow-regulating valve is typically a movable/positionable type of valve such as a linearly translatable valve. A valve of this design generally includes a valve body through which a flow passage is disposed. Other components include a plug member located within the flow passage and an elongated valve stem. The plug member is attached to the valve stem and the valve stem passes through a valve bonnet. Using the valve stem, the plug member can be linearly translated toward or away from a valve seat within the flow passage between a fully opened position and a fully closed position, and intermediate positions therebetween. The plug member blocks all flow when in the fully closed position and allows for maximum flow when in the fully opened position.
An actuator is often connected to the valve stem to linearly translate the plug member towards and away from the valve seat,. The actuator is typically located adjacent the valve bonnet and imparts linear translation motion to the valve stem. Accordingly, the valve stem will have to move with respect to the valve housing that it passes into. To prevent the undesirable loss of process fluids passing through the valve, the intersection between the reciprocating valve stem and the valve bonnet into which the stem passes should be well sealed. This is especially true where the process fluid is flammable and capable of potentially producing an explosion (e.g., natural gas, gaseous fuel), is poisonous, or is otherwise environmentally harmful.
Several devices and sealing methods have been proposed for sealing a linearly moving valve stem in a pressurized seal arrangement as disclosed in, for example, U.S. Pat. Nos. 6,161,835 and 5,746,435 to Arbuckle, U.S. Pat. Nos. 5,772,216 and 5,607,165 to Bredemeyer, and U.S. Pub. Applns. 2004/0135112 and 2004/0134665 to Greeb, et al., each of which is incorporated herein in its entirety by this reference. Such pressurized dynamic sealing arrangements may be used in the process gas industry for valves and the like to promote sealing and ensure that the process gas does not leak or produce a hazardous external environment. These patents disclose that using a pressurized barrier fluid or sealant (e.g., grease) provides opposing axial fluid forces on two spaced apart seals. In these arrangements, the barrier fluid has a pressure that is typically greater than a pressure of the process fluid. As such, if leakage is to occur, most or all of the leakage would be the barrier fluid rather than the process fluid since the barrier fluid is at the higher pressure of the two. Indicating mechanisms, which are disclosed in the above-noted patents, effectively indicate and inform a user whether leakage of the barrier fluid is occurring.
Unfortunately, the concepts disclosed in the Arbuckle and Bredemeyer patents are complex and costly to implement, have complex plumbing arrangements, are not practical to structurally implement, and/or require numerous complex components for establishing a preload barrier. Further, the indicating mechanism or indicators disclosed in at least some of these patents may have accuracy problems, may not readily indicate the exact source of the problem, and/or may be difficult or impractical to employ in the field or across different applications. Finally, these prior art concepts disclosed in the Arbuckle and Bredemeyer patents are subject to potential premature failure and leakage since they do not provide fully independent redundant seals in the sealing arrangements as well as an auxiliary (i.e., secondary) containment chamber to impound a leaking barrier fluid.